Aspects of the Infallibility of the Prophets and their necessity

The term 'isma is to be understood in the sense of inviolability and immunity. In the domain of prophecy it comprises the following aspects:

1. in respect of the station of receiving, preserving and conveying revelation;
2. in respect of being protected against all disobedience and sin;
3. in respect of being protected against error in both individual and social affairs.

As regards the first of these degrees (receiving, preserving and conveying revelation), there is universal agreement; for were there to be any likelihood of error or mistake at this degree, the trust of the people in the Prophet would be shaken, and they would not be able to rely upon the other messages of the Prophet; in consequence, the whole purpose of revelation would be undermined.

As regards the first of these degrees, there is universal agreement; for were there to be any likelihood of error or mistake at this degree, the trust of the people in the Prophet would be shaken, and they would not be able to rely upon the other messages of the Prophet; in consequence, the whole purpose of revelation would be 'undermined. The Holy Qur'an tells us that God has placed the Prophets under an all-encompassing supervision to ensure that the revelation is correctly conveyed unto mankind, as it is said:

[He is] Knower of the unseen, and He does not disclose His [knowledge of the] unseen to anyone. Except whom He has approved of messengers, and indeed, He sends before each messenger and behind him observers. That he may know that they have conveyed the messages of their Lord; and He has encompassed whatever is with them and has enumerated all things in number. (Sura al:Jinn, 72: 26- 28)

In these verses, two types of guardian are mentioned in regard to the function of protecting the integrity of the revelation: angels who guard the Prophet against every type of evil; and the Almighty Himself, who guards the Prophet and the angels. The reason for this comprehensive supervision is to ensure the realization of the purpose of prophecy, that is, that revelation be conveyed unto mankind.

In these verses, two types of guardian are mentioned in regard to the function of protecting the integrity of the revelation: angels who guard the Prophet against every type of evil; and the Almighty Himself, who guards the Prophet and the angels. The reason for this comprehensive supervision is to ensure the realization of the purpose of prophecy, that is, that revelation be conveyed unto mankind.

The Messengers of God are rendered immune from all types of sin and error

The Messengers of God are rendered immune from all types of sin and error in their enactment of the rulings of the Shari'a. For were they not absolutely in accord with the divine rulings which they themselves were propounding, nobody could rely upon the truth of their sayings, and in consequence the purpose of prophecy would not be fulfilled.
The sage Nasir al-Din Tusi has given a concise explanation of this proof of the necessity of 'isma:

"Isma is essential for the Messengers, in order that their sayings be trusted, and the purpose of prophecy be realized. '[1]

As for the Messengers being away from sin, many verses of the Qur'an stress this in different ways. We allude to some of these below.
1. The Qur'an refers to the Messengers as being guided and appointed by the Divine Reality:

... and We chose them and guided them unto a straight path. ( Sura al¬An 'am, 6:87)

2. It reminds us that whomsoever God guides, none can lead astray:

And whoever Allah guides - for him there is no misleader. Is not Allah Exalted in Might and Owner of Retribution? (Sura al-Zumar, 39:37)

3. 'Sin' is understood in the sense of 'misguidance':

Yet he hath led astray of you a great multitude. (Sura Ya Sin, 36:62)

These verses, taken together, show that the Messengers are devoid of all kinds of error and sin.

The intellectual proof

The intellectual proof of the necessity of the 'isma of the Messengers applies equally to the necessity of their 'isma prior to their receiving their prophetic mission. For one who has spent part of his life in sin and error and then afterwards claims to offer authentic guidance cannot be relied upon. But as for one who, from the very beginning of his life, was devoid of every type of impurity, such a person would elicit the trust of all people. Also, those who denied the truth of the message would all too easily be able to Point to the dark past of the Messenger, vilify his name and character, and thus undermine the message. In such an environment, only one who has lived a life of impeccable purity, such that he merits the title 'Muhammad the Trustworthy' (al-Amin), would be able, by the brilliance of his radiant personality, to cast aside the clouds of malicious propaganda generated by his enemies and, through an unwavering and noble rectitude, gradually illumine the murky ambience of the Jahiliyya Arabs.

One who has spent part of his life in sin and error and then afterwards claims to offer authentic guidance cannot be relied upon. But as for one who, from the very beginning of his life, was devoid of every type of impurity, such a person would elicit the trust of all people.

In addition to such considerations, it is clear that a man who was immune from sinning from the very beginning of his life is elevated above another who is only rendered such after having been appointed to a prophetic mission; and the scope of his guidance will, correspondingly, be much greater. Divine wisdom demands that only the best, most perfectly accomplished person be chosen as model and exemplar for humanity.

Other domains of the Prophet's infallibility

In addition to being incapable of sin, the Messengers are also immune from error in the following domains:
1. Judging disputes. The Messengers were charged by God to pass judgement according to the divinely-instituted scales of justice, and there could never be any question of the Messengers deviating in any way from the principles by which disputes and all other legal questions were to be ajudicated.
2. Specification of the boundaries of religious rulings: for example, ascertaining whether a given liquid is alcoholic or not.
3. The domain of social principles: for example, specifying what contributes to public welfare and what corrupts it.
4. The domain of conventional daily matters.
The reason for the 'isma operating in the last three domains is this: In the minds of most people, error in these matters implies error in the domain of religious rulings also. Consequently, committing error in such matters undermines the certainty that people must have in the personality of the Messenger, and leads ultimately to the undermining of the purpose of prophecy. However, the necessity of 'isma in the first two domains is more readily apparent than in the fourth.

1. Nasir al-Din Tusi, Tajrid al-itiqad, maqsad 4, mas'ala 1.